The invention relates to improvements in a two roller interparticle crushing high pressure roller press and the method of operating for the pressure treatment of granular material.
In the development of roller presses for pressing pulverulent material, a unique method and apparatus have been developed to provide for crushing by a method attaining interparticle crushing. In this interparticle crushing, unusually high nip pressures are utilized of at least 500 kg/cm.sup.2 between the rolls and this method is disclosed in U.S. Pat. No. 4,357,287 and German Patent DE-27 08 053, Schoenert and in a subsequent U.S. Pat. No. 4,703,897, Beisner et al. In the novel process of interparticle crushing, the pulverulent material supplied to the nip is crushed by the high pressures and crushing occurs between the particles of material forming incipient cracks within the material so that the material particles can be effectively further disintegrated with minimum energy. The advantage of the interparticle crushing is uniform improved crushing with a substantial reduced outlay of power required.
During operation of a high pressure roller press for interparticle crushing, the pulverulent bulk material is supplied to the nip and seized by the oppositely driven rollers and drawn into the nip by friction. This is a friction between the bulk material particles itself and friction between the bulk material and roller surface. The individual particles of the bulk material that are drawn in are mutually crushed in a product bed with the material compressed between the two roller surfaces with an extremely high pressure which has been known to the art as interparticle crushing and which is disclosed in the aforementioned U.S. and German patents. The products of this pressure treatment are agglomerates or scabs of comminuted bulk material that can be subsequently disintegrated with a minimum of mechanical power outlay.
Simultaneously with the formation of the agglomerates, the air that was originally present in the pulverulent bulk material is expressed from the product bed. It escapes through the material column formed by the bulk material being fed into the nip. As a result of the air escapement, the bulk material is loosened in the draw-in region between the rollers, particularly when the fine grained bulk materials are pressed. The result is that the material draw-in is deteriorated and the escape of air has an adverse effect in the draw-in. As a result, the throughput and the degree of comminution in the nip are lowered.
Efforts have been made to alleviate the problem of the escape of air and the disadvantageous results in that where high proportions of fine grained bulk material are used, the aeration problem is approached by German Published Application 38 06 398. This proposed that the product delivery stack be subdivided and the coarse material and fine material be separately supplied to the nip. By this arrangement, the coarse bulk material is kept so low that the air expressed therefrom can easily escape through the low and coarse pored bulk material.
A disadvantage in this disclosed method is that it can only be employed when the coarse material and the fine material are separated from one another before the pressure treatment. Further, the possibility of the formation of a nonuniform product bed cannot be precluded or occurs due to the separate delivery of coarse material and fine material.
A further disadvantage of known two roller machines is that high wall friction resistances impede the replenishment of the bulk material in the nip due to the lateral pressure of the bulk material supported at the bottom of the roller surfaces against the inside wall of the product delivery stack. This is especially true when the filling level in the product delivery stack is extremely high.